A prior-art device for measuring the concentration of a paramagnetic gas is described in DE 100 37 380 A1 and is characterized by a modulatable magnetic field source with an air gap, a modulation source for sending a modulation signal to the magnetic field source, a measuring element for generating a heat flux measurement signal, which is arranged at least partially within the air gap, is heated to a working temperature by a power source and by which a filter means connected to the measuring element for separating variations from the heat flux measured signal based on the modulation of the magnetic field, wherein the changing amplitude of the variations is an indicator of the percentage of the paramagnetic gas in the gas sample. The measurement of the oxygen concentration takes place in the air gap of an electrically modulatable magnet system, which air gap is equipped with a sample gas cuvette. On the one hand, it is difficult in the measuring systems used hitherto to prepare suitable coil cores with which the high magnetic flux densities in the air gap, which are necessary for a strong measured signal, can be generated with the sample gas cuvette in a reproducible manner. On the other hand, the narrow air gap must be prepared with geometric precision and very narrow tolerances for a reliable measurement. Finally, electric and magnetic interference fields shall be screened in order not to interfere with the measurement. Finally, mechanical protection of the measuring system is desirable. The current measuring arrangements are subject to these shortcomings.